Atomic force microscope tips are used to measure the topography of surfaces at an atomic level. In atomic force microscopy an atomic tip is scanned over a surface and the interactions between the few atoms at the end of the tip and the surface are recorded. The sharpness of the tip, or its radius of curvature, determines the resolution of the scan. Some atomic force microscope tips are formed at the edge of a cantilever. With cantilevered atomic force microscope tips the motion of the cantilever may be recorded to determine the topography of the surface being scanned. Atomic force microscopy may also be used in the manufacture of integrated circuits (IC) to measure the dimensions of components on the IC. There are also developments of applications for atomic force microscopy in the area of data storage. In this application shaper tips will enable a higher data density to be achieved since more data bits can be written per square area.
One method for forming atomic force microscope tips uses conventional electron beam chemical vapour deposition (CVD). This method as described in U.S. Pat. No. 5,611,942 involves first forming a rounded tip. Masks are then added to the tip in areas where points will be formed. The mask covered tip is then etched for a predetermined period of time. The etching process removes the tip material in a parabolic manner between the masks leaving points under the mask layers. Finally the mask layer is removed to reveal a multi-pointed atomic force microscope tip. One problem with this method is ensuring uniformity of the etching process to form uniform tips. A further problem is that the tips tend to break off before they are sharp, leaving a fractured end.
Another method for forming atomic force microscope tips is to etch pyramidal pits into silicon with an etchant such as potassium hydroxide (KOH). These pits are then used as a mould for a silicon nitride tip. Common materials deposited in the mould include polymers, silicon dioxide and silicon nitride. Any moulded tip formed in this manner must be separated from the mould. In addition to the difficulty in ensuring a clean separation of the tips from the moulds, this method may not be applicable to more complex types of MEMS (microelectromechanical) structures. Further to this tips formed from silicon have superior physical properties, such as high strength and stiffness, when compared to tips formed from other materials.